net/sfc: convert to new Tx offload API

net/sfc: convert to new Tx offload API

Ethdev Tx offloads API has changed since:
commit cba7f53b717d ("ethdev: introduce Tx queue offloads API")
This commit support the new Tx offloads API.

The code which fills in txq_flags in default_txconf is preserved
because rte_eth_dev_info_get() lacks conversion between offloads
and txq_flags fields which means that a legacy application which
relies on default_txconf will fail to configure Tx queues in the
case when some bits in txq_flags are mandatory.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Ferruh Yigit <ferruh.yigit@intel.com>